Impact of the ZnS layer position in a stacked precursor film on the properties of CZTS films grown on flexible molybdenum substrates

• Published in: Optical materials 2023-02, Vol.136, p.113423, Article 113423
• Main Authors: Yagmyrov, A., Erkan, S., Başol, B.M., Zan, R., Olgar, M.A.
• Format: Article
• Language: English
• Subjects: CZTS; Flexible substrate; Mo foil; RTP; Stacking order; Thin film solar cell
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2022.113423

In the present study, CZTS thin films were prepared by annealing and reaction of Cu–Sn–ZnS precursor layers. First, sputter deposition was carried out on flexible molybdenum (Mo) foil to form Mo-foil/CuSn/ZnS/Cu, Mo-foil/CuSn/Cu/ZnS and Mo-foil/ZnS/CuSn/Cu stacked precursor structures. Annealing process was performed in sulfur atmosphere using Rapid Thermal Processing (RTP) method to obtain kesterite CZTS phase in the reacted layers. All prepared precursors and CZTS thin films displayed Cu-poor and Zn-rich chemical composition, as targeted. XRD patterns of CZTS samples showed that the kesterite phase was obtained in all samples regardless of the stacking order of the precursor films. However, the full width at half maximum (FWHM) values of the (112) preferential peaks extracted from the XRD patterns, and the corresponding structural parameters (crystallite size and microstrain), indicated that the Mo-foil/ZnS/CuSn/Cu precursor structure yielded more promising crystalline quality. The occurrence of kesterite phase in all samples and existence of low amount of CTS phase were verified by Raman spectroscopy measurements. The CZTS sample prepared employing the Mo-foil/ZnS/CuSn/Cu precursor film structure presented more prominent, homogenous and compact surface microstructure as observed in SEM images. Optical band gap values were found to be in the range of 1.44–1.50 eV. The room temperature photoluminescence (PL) measurements showed that the transitions from the conduction band to intrinsic defect levels dominated the spectra instead of the band-to-band transitions. Electrical characterization of the films showed that Mo-foil/CuSn/ZnS/Cu and Mo-foil/ZnS/CuSn/Cu precursor films yielded lower electrical resistivity and higher carrier concentration due to better crystalline quality. Overall, it was seen that the CZTS thin films produced using the Mo-foil/ZnS/CuSn/Cu stacked precursor layers displayed better properties in terms of crystalline quality, surface microstructure, and optical and electrical properties, which are favorable for photovoltaic applications. •CZTS thin films were fabricated over Mo-foil substrates through reaction of stacks comprising ZnS, Cu and Sn layers.•Effect of stacking order on the properties of the resulting CZTS films was investigated.•Better crystal structure was observed in samples fabricated using Mo-foil/ZnS/Cu/Sn/Cu stack structure.•Optical band gap of films was found to be in the range of 1.44–1.5 eV.•Film obtained using the Mo